Mapping Alaska’s Mat-Su Basin

Why we love it

You don't have to look at the legend to understand what this map conveys. It depicts 28,000 miles of previously unmapped waterways and critical habitat in South Central Alaska’s Matanuska-Susitna (Mat-Su) Basin. Using gray scale and opacity to mask everything outside the study area, the map provides a clear delineation of the watershed boundaries. In contrast, vibrant colours within the basin successfully draw the reader in and keep the focus on the intended theme of the map.

Why it works

The Matanuska-Susitna Basin has a complex geography and dense hydrologic network of streams, rivers, and lakes. This map works by employing important techniques to present a striking view of the entire area. The map author uses colour masterfully to highlight and accentuate the most important elements. Additionally, only the most critical labels are provided for reference. As an observer, we get a clear and unimpeded representation of the Mat-Su Basin and its conglomerate of hydrologic features.

Important steps

Update dataset and choose symbology

Conduct a high-resolution (1:24K) update to the USGS National Hydrologic Dataset. Choose symbology for linear stream and areal lakes.

Use greyscale background to emphasis areas

Make the area “pop” with a greyscale background. The greyscale basemap is not a hillshade. It is a 90 m DEM shaded relief created with the image analysis window assigned greyscale colour ramp under the Esri Light Grey Canvas basemap and 50 percent transparency applied.

Requirements

Data

Datasets include the USGS NHD and NED, local LiDAR and IfSAR elevation data (conflated to the NED), the Mat-Su Borough and City of Anchorage, US Census data, and NOAA ENCs and bathymetric DEMs. TNC Alaska Science Director David Albert provided valuable cartographic advice.

Analysis

Primary analysis is the 2015 update to the USGS National Hydrographic Dataset which used the “ele-hydro” concept of elevation-derived flowline modeling to build the 53,000 lineal mile hydrologic network represented on the map.

Time

This map went through many iterations from 2014 to present. By the time it entered the 2016 Esri UC Map Gallery, roughly 400 hours had been spent on it.

Tips and tricks

Use image analysis window for raster datasets

When using raster datasets for cartographic purposes, rely heavily on the image analysis window and raster functions to hold data in memory rather than create new files.

Clip and mask your DEM to tell them apart

It can be difficult finding a single-color ramp to highlight varied topography in the same DEM. However, clip and mask portions of the DEM to assign individual color ramps to different topographic “categories” so no details are lost.

Add character to transitions with symbology

For areas of interest, which include an interface between terrestrial and Marine/Ocean areas, NOAA ENCs have a range of interesting symbology that can add character to the transition between bathymetric DEMs and elevation DEMs.